Armor plate



13 l i l v ntted Jan. 15, 1935 ABMOB PLATE Fritz Bittershauscn, Essen.Germany Fried. Krupp Aktiengesellachaft,

Ruhr, Germany acsiznor to Essen-on-th Y No Drawing. Application April30, 1982, Serial No. 608,566. In Germ 8 Claims.

hardened on one side and manufactured from a steel alloy theconstituents of which are so determined that, on heating, the lowercritical point (point AC1) has a comparatively high position so that theinterval of temperature existing between the lower and upper criticalpoint (AC1 to A03) is small. An armor plate of this kind consists. forinstance of a steel alloy containing about 0.2 to 0.65% carbon, about0.5 to 4% nickel, about 2.0 to 4.5% chromium and about 0.2 to 1.5%molybdenum, wherein the molybdenum may be replaced partly or wholly by a1.5 to 3-fold quantity of tungsten.

Steel alloys hitherto used for the manufacture of armor plates containabout 0.25 to 0.35% carbon, about 3 to5% nickel and about 1 to 1.8%chromium. In order to facilitate-the heat treatment, sometimesmolybdenum or tungsten or both these metals have been added to thesesteel alloys.

Now exhaustive tests have shown that the toughness of armor plates andtheir resistance to being injured by projectiles can be improved to anextraordinary extent by limiting the nickel content to 4% at the mostand at the same time increasing the chromium content to about 2 to 4.5%.Advantageously the percentage of nickel is determined according tothethiclmess of the armor plate, but it is of particular advantage tolimit the nickel content to not more than about 3% even with thethickest plates. With decreasing thickness of the plates the nickelcontent may be reduced. correspondingly, so as to amount with thinplates only to about 0.5%.

The armor plate forming the subject-matter of the invention isremarkable for the feature that, after having been brought to acondition of highest toughness by hardening and re-heat ing, it iscapable of being hardened on one side without cementation, but does notlose to an inadmissible extent its toughness on the non-hard,- enedside. With the armor plates of the known composition this is impossiblefor the following reasons: With the steel alloys the known armor platesare made from, the point A01 at which the transformation begins inheating the plate, lies between 650 and 700 0., whilst the practicallyrequired hardening temperature is about 850 C., that is nearly 200higher. New with' thin plates it is practically impossible to heat theplate on one side to a temperature of 850 C. and to keep the non-heatedside in a layer of sufficient depth at a temperature below the pointA01, that is about 200 0. lower. with anyJune 21, 1931 (Cl. 148-31) Thepresent invention relates to arm or plates plates such a heating .would"be possible, but there would be a broad layer which has a temperaturelying between the points A01 and A03 and therefore loses its toughnessafter the quenching and therefor acquires only insuiilcient hardness.Armor plates manufactured according to the invention behave otherwise.For, in

vthe new plates the point A01 is not only raised owing to the increasedchromium percentage and reduced nickel percentage, but also the-distancebetween the point Ac: and the hardening temperature, which lies abovethe point A03, is reduced. The increased carbon content acts in the samedirection. This small distance existing between the point Am and thehardening temperature in conjunction with the property of the chromiumsteels of easily being hardened makes it possible to harden the armorplates according to the invention at a temperature which lies about 50to C. above their point AC1, which lies at about 770 to 000 C. Such adifference of temperature, however, can be obtained also incomparatively thin plates so that it is possible to bring one side ofthe plate to hardening temperature and to maintain at the same time asufliciently thick layer of the other side at a temperature which isbelow the point A01, and therewith in the condition oi the highesttoughness, the transition layer which possesses less favorableproperties becoming considerably thinner than with the plates oi knowncomposition.

The heat treatment of the armor plates according to the inventionconsists in hardening. the plates from a temperature above the point Ac:and re-heating them to a temperature close below the point A01, wherebythe plates acquire highest toughness. As a consequence of this highre-heating temperature enabled by the high position of the point Am, adegree of toughness is obtained which could not be reached with theplates of the mown composition. Thereupon the plates are brought tohardening temperature only on the outer layer by heating them on oneside, and then hardened on this side by subsequent quick cooling. I

It is possible in itself of course, to cement the plates previous'tohardening, but this would involve certain technical and economicaldisadvantages.

The following examples forthe composition of armor plates forming thesubject-matter of the invention may be given:

1. Armor plate of about 100 mm. thickness, containing about: 0.38%carbon, 2.5% chromium.

1.3% nickel and 0.4% molybdenum.

2. Armor plate of about 150 mm. thickness, containing about: 0.45%carbon, 2.6% chromium, 1.8% nickel, and 0.45% molybdenum.

What I claim as my invention is:

1. Armor plates composed of a steel alloy having an A01 point of about770 C. or more and a hardening temperature not substantially over 100 0.above the A01 point, said alloy containing about 0.2 to 0.65% of carbon,0.5 to 3% of nickel, 2.0 to 4.5% of chromium, and 0.2 to 1.5% ofmolybdenum, the balance substantially iron, said plates being hardenedon the outside and having a strong tough layer on the inside, theintermediate band of softer steel being relatively-narrow.

2. Armor plates as described in claim 1, wherein the molybdenum contentis replaced at least partly by a 1.5 to 3 fold quantity of tungsten.

3. Armor plates composed of a steel alloy having an Ac1 point of about770 C. or more and a hardening temperature not substantially over 100 C.above the A01 point, said alloy containing about 0.2 to 0.65% of carbon,0.5 to 3% of nickel, 2.5 to 4.5% of chromium, and 0.2 to 1.5% ofmolybdenum, the balance substantially iron, said plates being hardenedon the outside and havin a strong tough layer on the inside, theintermediate band of softer steel being relatively narrow.

4. Armor plates as described in claim 3, wherein the molybdenum contentis replaced at least partly by a 1.5 to 3 fold quantity of tungsten.

5. Armor plates composed of a steel alloy having an Ac1 point of about770 C. or more and a hardening temperature not substantially over 100 C.above the A01 point, said alloy containing about 0.2 to 0.45% of carbon,0.5 to 3% of nickel, 2.0 to 4.5% of chromium, and 0.2 to 1.5% ofmolybdenum, the balance substantially iron, said plates being hardenedon the outside and having a strong tough layer on the inside, theintermediate band of softer steel being relatively narrow.

6. Armor plates as described in claim 5, wherein the molybdenum contentis replaced at least partly by a 1.5 to 3 iold quantity of tungsten.

7. Armor plates composed of a steel alloy having an A01 point of about770 C. or more and a hardening temperature not substantially over 100 C.above the A01 point, said alloy containing about 0.2 to 0.45% of carbon,0.5 to 3% of nickel, 2.5 to 4.5% of chromium, and 0.2 to 1.5% ofmolybdenum, the balance substantially iron, said plates being hardenedon the outside and having a strong tough layer on the inside, theintermediate band of softer steel being relatively narrow.

8. Armor plates as described in claim 7, wherein the molybdenum contentis replaced at least partly by a 1.5 to 3 fold quantity of tungsten.

" FRITZ RI'I'I'ERSHAUSEN.

